The present invention relates to an image forming apparatus and an image forming method for reading an image on an original and forming an image using electrophotography.
In a conventional digital electrophotographic image forming apparatus using electrophotography, an exposing unit, which comprises, in general, a semiconductor laser or an LED optical system, is used as means for writing an electrostatic latent image on a photosensitive body.
The exposing unit comprising the semiconductor laser uses one or more laser beams. The diameter of each beam is reduced by a converging lens, and a polygon mirror is operated to cause the beam to scan the entire surface of the photosensitive body, thereby writing image data thereon. Thus, there is no possibility of a variance in exposure amount, but the volume of the whole exposing unit increases due to the need to provide various lenses and mirrors.
On the other hand, the exposing unit comprising the LED optical system is advantageously suited to reduction in size, since its components are only LED elements and a substrate. However, it is difficult to realize uniform light emission by suppressing a variance in light amount among light-emitting elements.
Even where either of the above exposing units with the associated optical systems is used, it is difficult to form an optimal electrostatic latent image for reproduction of a low-density part, and so high-density picture dots are formed at a low resolution or an unstable electrostatic latent image is used. Consequently, image development becomes unstable, and toner is attached non-uniformly, leading to degradation in halftone graininess.
As a result, it is difficult to achieve both of good sharpness of a line part and graininess of a solid part, and a high-quality image cannot be formed.